‘this walk captures everything I love about Cambridge – a glorious ‘town and country’ mixture of  human and natural history’

The route: ‘through the fen edge town that became one of the world’s most famous cities’

3.1 miles (5 km) Walking guide time 1.5 hours plus stops

Known for its location on the River Cam and its nearby Chalk hills, Cambridge is still very much a fen edge city. Arriving in Cambridge from the north, along the River Cam, the Trail reaches the distinctive landscape feature of Castle Hill, the site of an early, and highly strategic, settlement that developed to become one of the world’s most iconic cities. This walk takes you down from the hill and across the ancient Magdalene Bridge, before winding along the river valley, past several colleges and providing quintessential views of the ‘Backs’. After passing through the characteristic ‘fens’ that still survive along the Cam, it finishes at the internationally important Sedgwick Museum of Earth Sciences.

Guiding you through what is now a mostly hidden landscape, the walk takes you back in time, giving a glimpse into the city’s past and the natural history of the area, from ‘Ice Ages’ to sub-tropical swamps and fenland rivers. You will discover how its natural character still filters through, seen in the riverside meadows, the numerous water channels, the subtle changes in the height of the land and even in the building stones used in many of its famous buildings.

Landscape and Geology 

The ‘high’ top of Castle Hill contrasts with the flat river terraces and floodplain in the valley of the River Cam. Except for small areas of Chalk and Gault on Castle Hill, and Gault by Vicar’s Brook, the bedrock on this walk is covered by much younger, river deposits. Now flowing south west to north east through the city, the river has changed its course a few times over the last c.500,000 years, during the Pleistocene ‘Ice Age’. The forces of ice and water have created a gradually deepening river valley with an often-changing pattern of channels. This has left a complex collection of sands and gravels (with some clay) that form a series of River Terraces. Four terraces have been broadly identified, representing different stages in the river’s history, with the oldest (the 4th) lying furthest from the river and (generally) at the highest elevation. The 4th Terrace gravels here date to c.300,000 ya when a large river flowed northwest (over Castle Hill), possibly through the ‘Oakington Gap’, and on to the Wash. The 3rd Terrace, under c.200,000 years old, formed during cold periods and, later, the warm Ipswichian Interglacial Stage, when a large floodplain developed in the valley. About 50,000 ya, the river was diverted to flow northeast leaving the 2nd Terrace gravels. The 1st Terrace dates from the end of the last glaciation, the Devensian, c.20,000 ya and narrowed the river near Castle Hill creating the crossing point that became so important years later. During the Holocene (the last 11,700 years), the river has left fine Alluvium over its floodplain, providing fertile pastures. When waterlogging persisted, Peat formed in low areas and still underlies parts of the river valley. Significant fossils have been found in the city including mammals from cold and warm stages of the Pleistocene: Hippopotamus, Horse, Bison, Reindeer, Woolly Mammoth, Woolly Rhino, Straight-tusked Elephant, Red Deer, Aurochs, Lion and Spotted Hyena.

Starting on the 4th Terrace capping Castle Hill, the walk descends onto the bedrock (Marly Chalk and Gault clay) before reaching the  Alluvium. After crossing the riverside 1st Terrace, it ‘climbs up’ onto the 2nd Terrace before returning to Alluvium along the river. After a brief walk on the 1st Terrace at Silver St, it returns again to Alluvium before following a narrow area of Gault, exposed due to erosion by Vicar’s Brook. Finally, you return to the 2nd Terrace on which much of the City centre lies, including the rest of the walk.